This application is filed under 35 U.S.C. xc2xa7371 from International Application PCT/JP00/08993, with an international filing date of Dec. 19, 2000, which claims the benefit of priority to Japanese Application No. 11-371820, filed Dec. 27, 1999, which are incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a polishing state monitoring method, polishing state monitoring device and polishing apparatus suitable for use in the planarization of semiconductor devices in a process in which semiconductor devices (such as ULSI devices, etc.) are manufactured, as well as a process wafer used in this polishing apparatus, a semiconductor device manufacturing method using this polishing apparatus, and a semiconductor device manufactured by this method.
2. Discussion of the Related Art
As semiconductor integrated circuits have become more highly integrated and smaller in size, processes required for the manufacture of such semiconductor integrated circuits have become more numerous and complicated. As a result, the surfaces of semiconductor devices are no longer always flat. The presence of step differences on the surfaces of semiconductor devices leads to wiring interruptions and local increases in resistance, etc., and thus causes circuit breaks and a drop in electrical capacitance. Furthermore, this also leads to deterioration of the withstand voltage and the occurrence of leakage in insulating films.
Meanwhile, as semiconductor integrated circuits have become more highly integrated and smaller in size, the light source wavelengths of semiconductor exposure apparatuses used in photolithography have become shorter, and the numerical apertures, or so-called NA, of the projection lenses of such semiconductor exposure apparatuses have become larger. As a result, the focal depths of the projection lenses of semiconductor exposure apparatuses have become substantially shallower. In order to handle such increased shallowness of the focal depth, it is necessary to flatten the surfaces of semiconductor devices to a greater degree than has previously been accomplished.
To describe this in concrete terms, a flattening technique such as that shown in FIGS. 11A1, 11A2, 11B1, and 11B2 has become essential in semiconductor processes. Here, a semiconductor device 24, an inter-layer insulating film 22 consisting of SiO2 and a metal film 23 consisting of A1 are formed on the surface of a silicon wafer 21. FIGS. 11A1 and 11A2 show examples in which the inter-layer insulating film 22 on the surface of the semiconductor device is flattened. FIGS. 11B1 and 11B2 show examples in which the metal film 23 on the surface of the semiconductor device is polished, so that a so-called xe2x80x9cdamascenexe2x80x9d is formed. Chemical mechanical polishing or chemical mechanical-planarization (hereafter referred to as xe2x80x9cCMPxe2x80x9d) has attracted attention as a method for the flattening of such semiconductor device surfaces.
CMP is a process in which irregularities in the surface of the wafer are removed by combining a chemical action (elution by means of a polishing agent or solution) with physical polishing; this process is an influential candidate for a global flattening technique. In concrete terms, a polishing agent called a xe2x80x9cslurryxe2x80x9d is used in which polishing particles (generally silica, alumina or cerium oxide, etc.) are dispersed in a medium such as an acid or alkali, etc., in which the object of polishing is soluble; polishing is caused to proceed by applying pressure to the wafer surface with a suitable polishing cloth, and grinding the surface by means of relative motion. Uniform polishing within the plane [of the surface] can be accomplished by making the application of pressure and speed of relative motion uniform over the entire surface of the wafer.
This process still suffers from many problems in terms of matching with conventional semiconductor processes, etc.; generally, a major problem that remains to be solved is monitoring of the polishing state (detection of the amount of polishing or polishing endpoint, etc.) while the polishing process is being performed (i.e., in-situ monitoring of the polishing state). There is a great demand for this in terms of improving the process efficiency as well.
In CMP, variations in the polishing rate occur as a result of local differences in the temperature distribution on the surface of the polishing pad and differences in the conditions of slurry supply, as well as differences in the pressure distribution. Furthermore, there are also differences in the polishing rate caused by variations in the surface conditions of the pad due to dressing, a drop in the polishing rate according to the number of wafers treated (deterioration caused by use) and individual differences in the pads used, etc. As a result of such problems, it is difficult to determine the endpoint of a specified amount of polishing by polishing time control.
Accordingly, methods have been proposed in which the endpoint is determined while measuring the motor torque or vibration, etc., in situ instead of determining the endpoint by time control. Such methods are somewhat effective in the case of CMP in which the material that is the object of polishing varies (e.g., CMP of wiring materials or CMP in which stopper layers are present). However, in the case of silicon wafers with complicated patterns, there is little variation in the material that is the object of polishing; accordingly, there may be instances in which determination of the endpoint is difficult. Furthermore, in the case of CMP of inter-layer insulating films, it is necessary to control the inter-wiring capacitance; accordingly, control of the residual film thickness is required rather than control of the polishing endpoint. It is difficult to measure the film thickness using methods that determine the endpoint by in-situ measurement of motor torque or vibration, etc.
Recently, therefore, monitoring of the polishing state (in-situ endpoint determination and in-situ film thickness measurement, etc.) by optical measurements, and specifically by the measurement of spectroscopic reflection, as described (for example) in Japanese Patent Application Kokai No. H11-33901, has been considered effective. In the case of such monitoring of the polishing state by the measurement of spectroscopic reflection, the wafer that is the object of polishing is irradiated with a probe light during CMP, and the amount of polishing or polishing endpoint is detected during polishing according to variations in the spectroscopic reflectivity of the light reflected from the wafer.
Light reflected from the polished surface of a wafer on which a semiconductor element is formed may be viewed as a superimposition of light waves from various layers and various parts of the device (laminated thin films); the waveform of the spectroscopic reflectivity varies according to the thickness of the layer that is being polished (i.e., the uppermost layer). This variation is stable (reproducible), and tends not to be affected by the interposed slurry, non-uniformity of the film thickness, or recesses and indentations in the surface or interfaces, etc. Accordingly, if the polishing state ascertained by measurement of the above-mentioned spectroscopic reflection is monitored, the wafer thickness, amount of polishing or polishing endpoint can be detected accurately in spite of the above-mentioned noise factors. Furthermore, the amount of polishing can be indirectly measured from the initial thickness of the wafer and the measured thickness of the wafer.
In the above-mentioned conventional monitoring of the polishing state by measurement of spectroscopic reflection, the measured spectrum which is the spectrum (intensity at various wavelengths) of the light reflected by the wafer indicates the spectroscopic reflectivity; accordingly, it would appear that the film thickness, etc., could be immediately determined from the measured spectrum.
In this case, however, the following problems arise:
Specifically, the measured spectrum is influenced not only by the thickness of the layer of the wafer that is being polished (i.e., the uppermost layer), but also by the spectroscopic characteristics of the light source emitting the probe light that irradiates the wafer. As a result, the waveform of the measured spectrum is disturbed according to the spectroscopic characteristics of the light source, so that the film thickness, etc., cannot always be determined with sufficient precision, thus making precise monitoring of the polishing state impossible. In addition, since the spectroscopic characteristics of the light source vary with elapsed time, the precision of monitoring of the polishing state drops as time passes.
Furthermore, since the measured spectrum is also influenced by the spectroscopic sensitivity characteristics of the light-receiving sensor that receives the reflected light, the waveform of the measured spectrum is also disturbed by these spectroscopic sensitivity characteristics, so that the precision of monitoring of the polishing state also drops in this regard as well. Moreover, since the spectroscopic sensitivity characteristics of the light-receiving sensor also vary with elapsed time, the precision of monitoring of the polishing state drops in this regard as well.
Furthermore, even though the precision tends not to be affected by the interposed slurry, it is desirable to reduce the effect of the interposed slurry even further in order to increase the precision of monitoring of the polishing state.
The present invention was devised in light of the above facts; one object of the present invention is to provide a polishing state monitoring method and polishing state monitoring device which make it possible to increase the precision of monitoring of the polishing state, and a polishing apparatus which uses this polishing state monitoring method and polishing state monitoring device.
Furthermore, another object of the present invention is to provide a process wafer which is suitable for realizing such a polishing state monitoring method.
In addition, another object of the present invention is to provide [a] a semiconductor device manufacturing method in which the process is made more efficient by monitoring the polishing state with good precision, so that semiconductor devices can be manufactured at a lower cost than in the case of conventional semiconductor device manufacturing methods, and [b] a low-cost semiconductor device.
The content of the present invention will be described below.
The invention is a polishing state monitoring method [a] in which the polishing state of an object of polishing which is polished by applying a load between a polishing body and this object of polishing in a state in which a polishing agent is interposed between this polishing body and object of polishing, and causing the polishing body and object of polishing to move relative to each other, is monitored during polishing, and [b] in which [i] the above-mentioned object of polishing is irradiated with a probe light emitted from a specified light source, [ii] a measured spectrum which is the spectrum of the light reflected by above-mentioned object of polishing is acquired during polishing, and [iii] the above-mentioned polishing state is monitored during polishing on the basis of the above-mentioned measured spectrum.
Furthermore, in this monitoring, a specified reflective body is irradiated with light emitted from the above-mentioned light source (for example, this light may be the same as the above-mentioned probe light, or may be light that is emitted from the above-mentioned light source and separately split from the probe light) either prior to the polishing of the above-mentioned object of polishing or during the polishing of the above-mentioned object of polishing, and a reference spectrum which is the spectrum of the light reflected by this reflective body is acquired; then, the above-mentioned polishing state is monitored during the polishing of the above-mentioned object of polishing on the basis of the relationship of the above-mentioned measured spectrum to the above-mentioned reference spectrum. Furthermore, light with numerous wavelength components such as white light, etc., is used as the above-mentioned probe light and the light that irradiates the above-mentioned reflective body.
It is desirable that the above-mentioned reflective body have flat spectroscopic characteristics; however, this reflective body may also have specified spectroscopic characteristics. In order to improve the S/N ratio of the measured spectrum that is acquired, it is desirable that the reflectivity of the above-mentioned reflective body be 20% or greater; a reflectivity of 30% or greater is even more desirable, a reflectivity of 50% or greater is more desirable yet, a reflectivity of 70% or greater is still more desirable, and a reflectivity of 90% or greater is even more desirable.
The above-mentioned relationship is a relationship in which the measured spectrum is replaced by a relative spectrum with the above-mentioned reference spectrum as a reference. The intensity ratio of the measured spectrum to the reference spectrum (i.e., the ratio of the intensity of the measured spectrum to the intensity of the reference spectrum at various wavelengths) may be cited as an example of the above-mentioned relationship; however, the present invention is not limited to such a relationship.
In the present invention, the above-mentioned measured spectrum is acquired during polishing, and the polishing state is monitored during polishing (in situ) on the basis of this measured spectrum; basically, therefore, monitoring of the polishing state based on the measurement of spectroscopic reflection is realized.
Furthermore, in the present invention, the measured spectrum is not used xe2x80x9cas is;xe2x80x9d instead, a specified reflective body is irradiated with light emitted from the probe-light light source either before polishing or during polishing, and the spectrum of the light reflected by this reflective body (reference spectrum) is acquired; then, the polishing state is monitored during polishing on the basis of the relationship of the measured spectrum to the reference spectrum.
Accordingly, even though the waveform of the measured spectrum itself is disturbed and caused to vary by the spectroscopic characteristics of the light source and changes over time, the reference spectrum and the measured spectrum are influenced in the same way by the spectroscopic characteristics of the light source; consequently, the effect of the spectroscopic characteristics of the light source can be more or less excluded from the above-mentioned relationship. Furthermore, if the respective beams of reflected light that are received when the measured spectrum and reference spectrum are acquired are received by the same light-receiving sensor, then the reference spectrum and measured spectrum are influenced in the same way by the spectroscopic sensitivity characteristics of the light-receiving sensor; accordingly, the effect of the spectroscopic sensitivity characteristics of the light-receiving sensor can be more or less excluded from the above-mentioned relationship. In the present invention, therefore, since the polishing state is monitored on the basis of the above-mentioned relationship, the precision of monitoring of the polishing state is increased.
Furthermore, in cases where the reference spectrum is acquired prior to polishing, it is desirable that this reference spectrum be acquired immediately prior to the initiation of polishing or at a point in time that is close to the point in time at which polishing is initiated, in order to exclude the effects of changes over time as far as this is possible. Of course, since changes over time in the spectroscopic characteristics of the light source or the light-receiving sensor do not appear in a short time, it is sufficient if the time from the acquisition of the reference spectrum to the initiation of polishing is a time which is short enough so that there is no conspicuous appearance of the effects of such changes over time.
Furthermore, examples of the above-mentioned polishing state include detection (or determination) of the remaining film thickness, amount of polishing or polishing endpoint.
The invention is characterized by the fact that in the invention the above-mentioned probe light and the above-mentioned light that is directed onto the above-mentioned reflective body are directed onto the above-mentioned object of polishing or the above-mentioned reflective body via one or more windows formed in the above-mentioned polishing body, or else the above-mentioned probe light and the above-mentioned light that is directed onto the above-mentioned reflective body are directed onto portions of the above-mentioned object of polishing or the above-mentioned reflective body that are exposed from the above-mentioned polishing body.
In the invention, windows may be present in or absent from the polishing body.
The invention is characterized by the fact that in the invention the above-mentioned reference spectrum is acquired in a state in which the above-mentioned polishing agent is interposed in the light path of the above-mentioned light that is directed onto the above-mentioned reflective body and the light path of the light that is reflected from this reflective body.
In the invention, the reference spectrum may also be acquired with no polishing agent interposed. However, if the polishing agent is interposed as in this invention, then a reference spectrum which shows the effects of the polishing agent can be acquired in a state that is close to the state in which the measured spectrum is acquired; accordingly, the effect of the polishing agent on the above-mentioned relationship (e.g., the effects of scattering and absorption caused by the polishing agent) can be reduced, so that the precision of monitoring of the polishing state can be further increased.
The invention is characterized by the fact that in the invention the above-mentioned reference spectrum is acquired in a state in which the above-mentioned polishing agent is interposed in the light path of the above-mentioned light that is directed onto the above-mentioned reflective body and the light path of the light that is reflected from this reflective body, and in which a load that is substantially the same as the load applied during the polishing of the above-mentioned object of polishing is applied between the above-mentioned polishing body and the above-mentioned reflective body.
In the invention, a load need not be applied between the polishing body and the reflective body at the time that the reference spectrum is acquired. However, if the reference spectrum is acquired while applying a load between the polishing body and the reflective body that is substantially the same as the load applied during the polishing of the object of polishing, as in this invention, then the thickness of the layer of the interposed polishing agent will also be similar to the thickness of the layer of the polishing agent at the time that the measured spectrum is acquired. Accordingly, in the present invention, a reference spectrum is acquired which reflects the effects of the polishing agent in a state that is much closer to the state that obtains when the measured spectrum is acquired than is the case in the invention; accordingly, the effect of the polishing agent on the above-mentioned relationship can be further reduced, so that the precision of monitoring of the polishing state can be increased even further.
The invention is characterized by the fact that in the invention the above-mentioned reference spectrum is acquired while the above-mentioned polishing agent is interposed in the light path of the above-mentioned light that is directed onto the above-mentioned reflective body and the light path of the light that is reflected from this reflective body, and while the above-mentioned reflective body is polished under substantially the same conditions as the polishing conditions used for the polishing of the above-mentioned object of polishing.
In the invention, the reflective body need not be polished at the time that the reference spectrum is acquired. However, if the reference spectrum is acquired while the reflective body is polished under substantially the same conditions as the polishing conditions used for the polishing of the object of polishing, as in the present invention, then the effects of variations in the thickness of the layer of polishing agent according to the polishing conditions, and the effects of bubbles that are admixed during the relative motion of the object of polishing and the polishing body, etc., will also be reflected in the reference spectrum. Accordingly, the present invention allows the acquisition of a reference spectrum that reflects the effects of the polishing agent in a state that is much closer to the state that obtains when the measured spectrum is acquired. Consequently, the effects of the polishing agent on the above-mentioned relationship are further reduced, so that the precision of monitoring of the polishing state is increased even further.
The invention is characterized by the fact that in any of the inventions the above-mentioned reflective body or a member which has this reflective body has substantially the same shape and dimensions as the above-mentioned object of polishing.
In the inventions, there are no particular limitations on the shape and dimensions of the reflective body or member which has the reflective body. In the present invention, however, the reflective body or member which has the reflective body can be handled in the same manner as the object of polishing, which is desirable.
Furthermore, in the inventions, there are no particular limitations on the reflective body; for example, this reflective body may consist of a mirror which is formed by forming a metal film that has the above-mentioned reflectivity, or a mirror-finished plate (e.g., a metal plate or mirror-finished silicon wafer, etc.). Such members are also suitable as the reflective body used in the present invention.
The invention is characterized by the fact that in the invention the above-mentioned object of polishing is a process wafer, [b] the above-mentioned reflective body or the above-mentioned member is also held beforehand in the container that accommodates the above-mentioned process wafer during the waiting period, and [c] the above-mentioned reflective body or the above-mentioned member is set in a specified polishing position at the time of acquisition of the above-mentioned reference spectrum using a device which sets the above-mentioned process wafer in the above-mentioned specified polishing position from the above-mentioned container.
In the present invention, the reflective body or member which has the above-mentioned reflective body can be handled in the same manner as the process wafer; accordingly, acquisition of the reference spectrum is simplified, which is desirable.
The invention is characterized by the fact that in any of the inventions the above-mentioned reflective body is installed in the holding part that holds the above-mentioned object of polishing during polishing.
If the reflective body is installed in the holding part that holds the object of polishing as in the present invention, then there is no need for a stage in which the reflective body is set in the polishing position when the reference spectrum is acquired. Furthermore, it becomes possible to acquire the reference spectrum during polishing.
The invention is characterized by the fact that in any of the inventions the above-mentioned object of polishing is a process wafer, and the above-mentioned reflective body is formed in an area of this process wafer other than the device areas (i.e., in a so-called dummy area).
In this case, for example, the reflective body can be formed as a so-called dummy cell in which a film of a metal that has the above-mentioned reflectivity is formed. The area in which the reflective body is formed may be a large area corresponding to one chip, or may be a smaller area.
If the reflective body is formed on the process wafer itself (which constitutes the object of polishing) as in the present invention, there is no need for the separate preparation of a reflective body.
The invention is a process wafer in which [a] a reflective body is formed on the side of the polished surface in an area other than the device areas, and [b] the size of the area in which the above-mentioned reflective body is formed is larger than the light spot that is directed onto the above-mentioned reflective body in order to acquire the reference spectrum (which is the spectrum of the light reflected by the above-mentioned reflective body).
The invention is a polishing state monitoring device which monitors the polishing state of the above-mentioned object of polishing using the polishing state monitoring method of any of the inventions. The present invention makes it possible to achieve highly precise monitoring of the polishing state in the same manner as in the inventions.
The invention is a polishing apparatus which is equipped with a polishing body and a holding part that holds the object of polishing during polishing, and in which the above-mentioned object of polishing is polished by applying a load between the above-mentioned polishing body and the above-mentioned object of polishing and by causing the relative motion of this polishing body and object of polishing in a state in which a polishing agent is interposed between the above-mentioned polishing body and the above-mentioned object of polishing. This polishing apparatus is equipped with the polishing state monitoring device that constitutes the invention. Since the present invention is equipped with the polishing state monitoring device that constitutes the invention, the polishing state can be monitored with good precision; as a result, the polishing process can be made more efficient.
The invention is a polishing apparatus which is equipped with a polishing body and a holding part that holds the object of polishing during polishing, and in which the above-mentioned object of polishing is polished by applying a load between the above-mentioned polishing body and the above-mentioned object of polishing and by causing the relative motion of this polishing body and object of polishing in a state in which a polishing agent is interposed between the above-mentioned polishing body and the above-mentioned object of polishing. In this polishing apparatus, the reflective body is disposed on the above-mentioned holding part so that this reflective body faces the same side as the side on which the above-mentioned object of polishing is held.
In the present invention, since the reflective body is held in the holding part, a polishing state monitoring device can be provided which is suitable for realizing the polishing state monitoring method that constitutes the invention.
The invention is a semiconductor device manufacturing method which has a process in which the surface of a semiconductor wafer is flattened using the polishing apparatus constituting the invention.
In the present invention, the process is made more efficient by monitoring the polishing state with good precision; as a result, semiconductor devices can be manufactured at a lower cost than in conventional semiconductor device manufacturing methods.
The invention is a semiconductor device which is manufactured by the semiconductor device manufacturing method constituting the invention. This invention makes it possible to provide a low-cost semiconductor device.
In cases where a metal is used as the above-mentioned reflective body in the respective inventions described above, examples of appropriate metals include Al, W, Cu, Pt, Si, Ag, Cr, Ni and stainless steel, etc.
As was described above, the present invention can provide a polishing state monitoring method and device which make it possible to improve the precision of monitoring of the polishing state, as well as a polishing apparatus which uses this monitoring method and device.
Furthermore, the present invention can provide a process wafer which is suitable for realizing such a polishing state monitoring method.
Moreover, the present invention can provide [a] a semiconductor device manufacturing method in which the process efficiency is increased by monitoring the polishing state with good precision, so that semiconductor devices can be manufactured at a lower cost than in conventional semiconductor device manufacturing methods, and [b] a low-cost semiconductor device.